How to Make It
Preheat oven to 400°F.
Combine ice water, vinegar, vanilla, and 1/3 cup flour in a small bowl; stir with a fork until well blended to form a slurry.
Whisk together hazelnut meal, salt, 2 tablespoons sugar, and remaining 1 1/3 cups flour in a medium bowl. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add slurry; stir just until moist. Turn dough out onto a lightly floured surface; knead lightly 5 times. Gently press dough into a 4-inch circle on heavy-duty plastic wrap. Cover with additional plastic wrap. Carefully roll dough into a 12-inch round; freeze 10 minutes.
Remove dough from freezer; remove and discard top piece of plastic wrap. Let stand until pliable, about 1 minute. Invert dough round onto a baking sheet lined with parchment paper; remove and discard remaining plastic wrap.
Stir together cornstarch and 2 tablespoons sugar; sprinkle over dough, leaving a 2-inch border around edge. Arrange peaches in a spokelike pattern on cornstarch mixture, leaving a 2-inch border around edge. Fold edges of dough over peaches, pinching gently to close any cracks.
Stir together preserves and honey in a small microwave-safe bowl; microwave at HIGH until soft, about 20 seconds. Brush preserves mixture over peaches and dough edges. Sprinkle dough edges with remaining 1 1/2 teaspoons sugar.
Bake at 400°F until crust browns, about 35 minutes. Remove from oven; sprinkle with thyme. Cool 10 minutes, and slice into 8 wedges.